T11E NAUTILUS. 53 



periphery, and usually several narrower bands above it and on the 

 base. 



Alt. 8.7, diam. 11 rum., whorls 5. 



Alt. 7, diam. 9.7 mm., whorls 4^. 



Alt. 7, diam. 9.3 mm. 



Alt. 8, diam. 9 mm. 



Shell Creek Canyon, 10 miles northeast of Shell, Wyoming, type 

 and cotypes no. 106977 A. N. S. P., also 106979 A. N. S. P. (dead 

 shells from type loc. ). Also in coll. University of Colorado. It 

 was found also in White Creek Canyon, 8 miles east of Shell, in 

 very damp pine forest. Collected by Don W. Walker. 



" Mr. Walker, who collected the Wyoming material, says the 

 Shell Creek pygmaea and cooperi were found together on a steep 

 slope on the south side of the canyon, where they occurred in great 

 numbers, more of the small ones below and more of the cooperi 

 above " (Henderson). It was found with 0. cooperi also in White 

 Creek Canyon. 



This snail is exactly intermediate between 0. cooperi (W. G. B.) 

 and 0. peripherica (Ancey). The irregular costulae or wrinkles are 

 stronger than in the first, but weaker and less regular than in 0. 

 peripherica. Further collections in Wyoming may show that 0. 

 pygmaea connects with one or the other of these species, but at pres- 

 ent it seems best to rank it as a distinct species, since this course is 

 more likely to insure critical examination into its status by those 

 who may secure further material. Moreover, its occurrence in com- 

 pany with 0. cooperi disposes of the hypothesis that pygrncza is a 

 stunted or unfavorable-station form of cooperi an idea which I 

 would otherwise have been inclined to harbor. It is readily distin- 

 guishable from young or small cooperi by the far greater convexity 

 of the whorls of the spire, as well as by the sculpture. As I have 

 seen a great number of 0. cooperi from many places, it does not 

 seem likely that intergrading forms occur. 



0. cooperi minor (Ckll.) is a larger form than pygmtza, having 

 less convex whorls, and the other characters of cooperi, of which it 

 is, as the name implies, merely a somewhat diminutive race. Speci- 

 mens from Mr. Henderson, taken at McCoy, Colo., and identified 

 by Professor Cockerell as his var. minor, have been compared. 



0. peripherica (Anc.) is the prior specific name to include the 

 series of local races described as var. binneyi, newcombi, multicostata, 



